Duncan establishes a portal
After several years of experimenting with Duncan in the Montauk Chair, Nichols claims that they could reliably travel to other times and places (even to Mars). Eventually, they were able to program Duncan with some basic commands so that the poor kid didn't need to be confined to the chair all the time. How kind.
At one point, however, Nichols' superiors told him to turn on the Montauk Chair and leave it running... through August 12th, 1983. As the story goes, by having another time-travel machine switched on, the Montauk Project successfully created a time wormhole to 1943, with power at both ends. That's how Ed and the Duncan Cameron of 1943 came through the portal, and that events described by Al Bielek occurred.